Application of PdCeO-based catalysts prepared by co-precipitation method in methane combustion

Abstract

The present invention relates to the use of a PdCeO-based catalyst prepared by a co-precipitation method in methane combustion. The catalyst is based on the rare earth oxide CeO2 and combines Pd with another transition metal element. A Pd-Ce-O-containing composite oxide catalyst is prepared by a co-precipitation method. Based on the total weight of the catalyst, the mass percentage of Pd is 0.1-5%, and the content of other metal elements is 0.5-10%. This Pd-Ce-O-containing composite oxide catalyst has the characteristics of high catalytic methane combustion activity and simple preparation. It has excellent catalytic reaction performance in methane combustion reactions under conditions close to industrial conditions.

Description

Technical Field

[0001] The present invention belongs to the field of industrial application and relates to the preparation of a catalyst and the study of its activity on methane combustion. Specifically, it relates to the preparation of a PdCeO-based composite oxide methane combustion catalyst and the study of its application in low-concentration methane combustion reactions. Background Art

[0002] Due to its potent greenhouse effect, methane's catalytic removal is crucial in treating methane-fueled vehicle exhaust and power plant exhaust. Due to its symmetrical molecular structure and high C-H bond energy, methane's catalytic combustion often requires a high ignition temperature or efficient catalysis. The temperatures of vehicle and power plant exhaust are insufficient to support spontaneous combustion of methane, making highly active catalysts essential for practical applications.

[0003] Methane combustion catalysts use the precious metal palladium as the primary active component. Due to its high unit price and limited reserves, palladium must be loaded onto a high-surface-area support, commonly used as gamma-phase activated alumina, to achieve high utilization. Furthermore, oxygen storage / release components are essential for treating vehicle exhaust, commonly used as ceria-based composite oxides. Vehicle exhaust has a complex composition, often containing CO, NO, and other hydrocarbon pollutants such as propylene and propane in addition to methane. Simultaneous catalytic elimination of all these pollutants requires precisely matched oxygen concentrations. However, exhaust oxygen levels often fluctuate widely, making it difficult to achieve optimal oxygen stability even with the combined efforts of oxygen sensors and appropriate intake control systems. Therefore, an oxygen storage / release component is required in the catalyst. Its principle is to store oxygen when oxygen levels are high and release it when they are low. Therefore, a large oxygen storage / release capacity is beneficial for suppressing oxygen fluctuations, and incorporating precious metals such as palladium into ceria can improve this capacity. Therefore, comprehensively speaking, in the treatment of motor vehicle exhaust containing methane, the active component Pd, the carrier alumina, the oxygen storage and release component CeO2, etc. are all indispensable.

[0004] The impregnation method is commonly used in the preparation of these catalysts. For example, a carrier such as alumina and CeO2 is mixed with water to form a slurry. After mixing, a Pd precursor solution is then added dropwise. Stirring allows for adsorption, followed by drying and calcination to obtain the finished catalyst. While the impregnation method is ideal for alumina, for CeO2-based oxides, while it can improve oxygen storage and release capacity, it has little effect on the methane ignition process.

[0005] To fully utilize the active Pd component bound to CeO2, a specially structured Pd-CeO2 catalyst system needs to be constructed. To this end, Sara Colussi et al. (Angew. Chem. Int. Ed., 2009, 48, 8481) used a solution combustion method, Maila Danielis et al. (Angew. Chem. Int. Ed., 2018, 57, 10212) used a dry ball milling method, and Honggen Peng et al. (Angew. Chem. Int. Ed., 2018, 57, 8953) utilized the self-assembly of an active agent, organosilane, Ce, and Pd sources, all achieving excellent catalytic performance. However, the industrial production process of the catalyst must simultaneously meet the requirements of high quality, low cost, easy scalability, and environmental friendliness. Therefore, simple improvements to existing production processes are more feasible.

[0006] Therefore, in order to simplify the catalyst preparation process and ensure the high catalytic performance of the Pd-CeO2 component, this patent aims to invent a Pd-CeO2-based composite oxide methane combustion catalyst prepared by a co-precipitation method. Summary of the Invention

[0007] In view of the above-mentioned state of the art, an object of the present invention is to provide a highly efficient catalyst component, a Pd-CeO2-based oxide system, for catalytically eliminating methane, an inert component in motor vehicle exhaust. This catalyst component has the characteristics of high ignition activity.

[0008] Another object of the present invention is to provide a method for preparing the catalyst of the present invention, which improves the utilization rate of the main active component Pd of the catalyst, thereby reducing the cost of the catalyst.

[0009] To achieve this objective, the present invention utilizes CeO2 as the primary component and co-dopes Pd and another transition metal into the CeO2 via a coprecipitation method. By properly controlling the conditions, the Pd and transition metal can be fully or partially incorporated into the CeO2 lattice. The catalytic combustion of methane is then performed under conditions simulating low-concentration methane found in vehicle exhaust.

[0010] The present invention provides a Pd-CeO2 based composite oxide methane combustion catalyst prepared by co-precipitation method, with a specific surface area greater than 100m 2 / g.

[0011] The catalyst comprises an active component comprising 0.5-5% by weight of Pd, based on the total weight of the catalyst. Pd is combined with another transition metal, such as Zr, Cu, Mn, Fe, Co, or Ni, preferably Zr, Cu, or Mn, with the weight percentage being 0.5-10%. Furthermore, the weight percentage of Pd is preferably 0.5-2%.

[0012] The present invention provides a Pd-CeO2-based composite oxide methane combustion catalyst prepared by a co-precipitation method, wherein the preparation method comprises the following steps:

[0013] 1) Dissolve all metal element precursors in water simultaneously, and the total concentration of metal precursors reaches 0.25-2.5 mol / L;

[0014] 2) adding a precipitant to a final concentration of 0.5-10 mol / L and stirring to obtain a precipitate;

[0015] 3) The precipitate is washed with water or directly dispersed into a treatment liquid (water, methanol or ethanol, etc.);

[0016] 4) After drying and calcining at 350-700° C. for 1-5 hours, the PdCeO-based composite oxide methane combustion catalyst prepared by the co-precipitation method is obtained.

[0017] The precursor of the active component Pd in the catalyst of the present invention is a Pd-containing acid or salt, such as one or two of palladium nitrate, palladium chloride, tetraammine palladium nitrate, and chloropalladic acid, preferably palladium nitrate. The precursor of the other metal active component is at least one of a nitrate, acetate, sulfate, or chloride containing the other metal, preferably a nitrate. The precipitant is at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, ammonium carbonate, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0018] The Pd-CeO2-based composite oxide methane combustion catalyst prepared by the above method requires no pretreatment before use. Its characteristic reaction conditions are: a methane-containing motor vehicle exhaust gas composition with a reaction gas volume ratio of 0.01-2% CH4 and 0.1-20% O2; the remainder is N2 or other inert gas.

[0019] According to the above gas volume ratio, the optimal reaction conditions of the Pd-CeO2-based composite oxide methane combustion catalyst are as follows: mass space velocity of 60,000 mL / h / g, reaction temperature of 400-500°C, and methane conversion rate>95%.

[0020] This Pd-Ce-O composite oxide catalyst has the characteristics of high catalytic methane combustion activity and simple preparation. It has excellent catalytic reaction performance in methane combustion reactions under conditions close to industrial conditions.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The Pd-CeO2-based composite oxide methane combustion catalyst prepared in the present invention, wherein the addition of palladium can effectively enhance the activity of the CeO2-based oxide in catalyzing methane ignition, thereby achieving the purpose of effectively utilizing the active component palladium.

[0023] 2. The catalyst of the present invention is simple to prepare and requires little modification to the existing preparation process.

[0024] 3. The catalyst does not need to be pretreated during the catalytic reaction, which simplifies the catalyst treatment process.

[0025] The present invention is described in detail below by way of specific embodiments. It should be noted that these embodiments are merely illustrative and do not constitute any limitation on the spirit and scope of the present invention. The present invention can be implemented as long as the conditions set forth in the Summary of the Present Invention are met. Therefore, the scope of protection of the present invention shall be subject to the claims of the application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are the ignition curves and X-ray diffraction spectra of methane combustion catalyzed by the catalysts in Example 1 and Comparative Examples 1 and 2; a is the ignition curves of methane combustion of samples 1, 5, and 6, and b is the X-ray diffraction spectra of samples 1, 5, and 6.

[0027] Figure 2 These are the ignition curves of methane combustion catalyzed by the catalysts in Example 2 and Comparative Example 3.

[0028] Figure 3 These are the ignition curves of methane combustion catalyzed by the catalysts in Examples 3 and 4.

[0029] Figure 4 These are the ignition curves and X-ray diffraction spectra of methane combustion catalyzed by each catalyst in Example 3 and Comparative Example 4; a is the ignition curve of methane combustion of samples 8 and 3, and b is the X-ray diffraction spectra of samples 8 and 3.

[0030] Figure 5 These are the ignition curves and X-ray diffraction spectra of methane combustion catalyzed by each catalyst in Example 1 and Comparative Example 5; a is the ignition curve of methane combustion of samples 9 and 1, and b is the X-ray diffraction spectra of samples 9 and 1. DETAILED DESCRIPTION

[0031] Example 1.

[0032] PdCeMnO catalyst prepared by co-precipitation method:

[0033] At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of 50wt% manganese (II) nitrate solution were dissolved in 3g of water. A palladium nitrate solution containing 10mg of Pd (15.4% by mass) was added to the above solution and stirred to obtain solution A. 1.2g of NaOH was dissolved in 30g of water to obtain solution B. With stirring, solution A was poured into solution B and stirred at room temperature for 30 minutes. The precipitate was centrifuged, washed three times with water, dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 2h to obtain the product, which was labeled as sample 1.

[0034] Example 2.

[0035] PdCeZrO catalyst prepared by co-precipitation method:

[0036] At room temperature (~25°C), weigh 1.63g of cerous nitrate hexahydrate and 0.87g of zirconyl nitrate and dissolve them together in 3g of water. Add a palladium nitrate solution containing 10mg of Pd element (the mass percentage of Pd element is 15.4%) to the above solution and stir evenly to obtain solution A. Weigh 1.2g of NaOH and dissolve it in 30g of water to obtain solution B. Pour solution A into solution B while stirring and stir at room temperature for 30 minutes. After centrifugation and washing the precipitate with water three times, dry it at 80°C overnight, and then calcine it at 500°C in a muffle furnace for 2h to obtain the product, which is marked as sample 2.

[0037] Example 3.

[0038] PdCeMnO catalyst prepared by co-precipitation method with sodium bicarbonate:

[0039] At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of 50wt% manganese (II) nitrate solution were dissolved in 30g of water. A palladium nitrate solution containing 10mg of Pd element (the mass percentage of Pd element is 15.4%) was added to the above solution A and stirred evenly to obtain solution A. 2.52g of NaHCO3 was weighed and dissolved in 30g of water to obtain solution B. With stirring, solution B was poured into solution A and stirred at room temperature for 30 minutes. The precipitate was centrifuged and washed with water three times, then ultrasonically dispersed in 30g of ethanol for 30 minutes, dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 2h to obtain the product, which was labeled as sample 3.

[0040] Example 4.

[0041] PdCeMnO catalyst prepared by co-precipitation method with sodium hydroxide:

[0042] Compared with Example 3, the preparation process was modified as follows: At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of 50wt% manganese (II) nitrate solution were weighed and dissolved in 30g of water. A palladium nitrate solution containing 10mg of Pd element (the mass percentage of Pd element was 15.4%) was added to the above solution A and stirred evenly to obtain solution A. 2.4g of NaOH was weighed and dissolved in 30g of water to obtain solution B. With stirring, solution B was poured into solution A and stirred at room temperature for 30 minutes. The precipitate was centrifuged and washed with water three times, then ultrasonically dispersed in 30g of ethanol for 30 minutes, dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 2h to obtain the product, which was labeled as sample 4.

[0043] Example 5

[0044] Activity evaluation of sample 1:

[0045] Catalytic reaction conditions: fixed bed microreactor, raw gas composition volume ratio of 0.5% CH4, 2% O2, He as balance gas, raw gas space velocity of 60,000 mL / h / g.

[0046] Reaction temperature range: linearly increase the temperature at a rate of 10℃ / min, and test the ignition curve within 50℃~500℃.

[0047] Example 6.

[0048] Activity evaluation of sample 2: the same conditions as in Example 5.

[0049] Example 7.

[0050] Activity evaluation of sample 3: the same conditions as in Example 5.

[0051] Example 8.

[0052] Activity evaluation of sample 4: the same conditions as in Example 5.

[0053] Comparative Example 1.

[0054] Pd / CeMnO catalyst prepared by impregnation method (twice calcined):

[0055] Compared to Example 1, the preparation process was modified as follows: At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of a 50wt% manganese(II) nitrate solution were dissolved in 3g of water to obtain Solution A. 1.2g of NaOH was dissolved in 30g of water to obtain Solution B. Solution A was poured into Solution B with stirring and stirred at room temperature for 30 minutes. The precipitate was centrifuged, washed three times with water, dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 2h to obtain the CeMnO support. 0.26g of CeMnO was dispersed in 5g of water. After uniform dispersion, a palladium nitrate solution containing 2.62mg of Pd (15.4% by weight of Pd element) was added with stirring. The mixture was evaporated to dryness at 80°C with stirring and then calcined in a muffle furnace at 500°C for 2h to obtain the product, designated Sample 5.

[0056] Comparative Example 2.

[0057] Pd / CeMnO catalyst prepared by impregnation method (single calcination):

[0058] Compared with Example 1, the preparation process was modified as follows: At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of 50wt% manganese(II) nitrate solution were dissolved in 3g of water to obtain solution A. 1.2g of NaOH was dissolved in 30g of water to obtain solution B. Solution A was poured into solution B with stirring and stirred at room temperature for 30 minutes. The precipitate was centrifuged, washed three times with water, and dried at 80°C overnight to obtain the supported CeMnO precursor. 0.26g of the CeMnO precursor was dispersed in 5g of water. After uniform dispersion, a palladium nitrate solution containing 2.62mg of Pd (15.4% by weight of the Pd element) was added with stirring. The mixture was evaporated to dryness at 80°C with stirring and then calcined in a muffle furnace at 500°C for 2h to obtain the product, which was labeled as sample 6.

[0059] Comparative Example 3.

[0060] Pd / CeZrO catalyst prepared by impregnation method:

[0061] Compared to Example 2, the preparation process was modified as follows: At room temperature (~25°C), 1.63g of cerous nitrate hexahydrate and 0.87g of zirconyl nitrate were dissolved in 3g of water to obtain Solution A. 1.2g of NaOH was dissolved in 30g of water to obtain Solution B. Solution A was poured into Solution B with stirring and stirred at room temperature for 30 minutes. The precipitate was centrifuged, washed three times with water, dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 2h to obtain the CeZrO support. 0.26g of the CeZrO support was dispersed in 5g of water. After uniform dispersion, a palladium nitrate solution containing 2.62mg of Pd (15.4% by mass of Pd element) was added with stirring. The mixture was evaporated to dryness at 80°C with stirring, and then calcined in a muffle furnace at 500°C for 2h to obtain the product, which is labeled Sample 7.

[0062] Comparative Example 4.

[0063] PdCeMnO catalyst prepared by co-precipitation with sodium bicarbonate (water washed):

[0064] Compared with Example 3, the preparation process was modified as follows: At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of 50wt% manganese (II) nitrate solution were dissolved in 30g of water. A palladium nitrate solution containing 10mg of Pd element (the mass percentage of Pd element was 15.4%) was added to the above solution A and stirred to obtain solution A. 2.52g of NaHCO3 was weighed and dissolved in 30g of water to obtain solution B. With stirring, solution B was poured into solution A and stirred at room temperature for 30 minutes. The precipitate was centrifuged, washed with water three times, and dried at 80°C overnight. It was then calcined in a muffle furnace at 500°C for 2h to obtain the product, which was labeled as sample 8.

[0065] Comparative Example 5.

[0066] PdCeMnO catalyst prepared by co-precipitation method with sodium hydroxide (without water washing):

[0067] Compared with Example 1, the preparation process was modified as follows: At room temperature (~25°C), 2.73g of cerous nitrate hexahydrate and 0.43g of 50wt% manganese (II) nitrate solution were dissolved in 3g of water. A palladium nitrate solution containing 10mg of Pd element (the mass percentage of Pd element was 15.4%) was added to the above solution and stirred to obtain solution A. 1.2g of NaOH was dissolved in 30g of water to obtain solution B. With stirring, solution A was poured into solution B and stirred at room temperature for 30 minutes. The precipitate was collected by centrifugation, dried at 80°C overnight, and then calcined in a muffle furnace at 500°C for 2h to obtain the product, which was labeled as sample 9.

[0068] Comparative Example 6.

[0069] Activity evaluation of sample 5: the same conditions as in Example 5.

[0070] Comparative Example 7.

[0071] Activity evaluation of sample 6: the same conditions as in Example 5.

[0072] Comparative Example 8.

[0073] Activity evaluation of sample 7: the same conditions as in Example 5.

[0074] Comparative Example 9.

[0075] Activity evaluation of sample 8: the same conditions as in Example 5.

[0076] Comparative Example 10.

[0077] Activity evaluation of sample 9: the same conditions as in Example 5.

[0078] The sample preparation conditions in each embodiment and comparative example are as follows Table 1:

[0079]

[0080] Corresponding Pd content and ignition temperature T 10 (Temperature to reach 10% conversion rate) The results are shown in Table 2 below:

[0081]

[0082]

[0083] 1 The mass percentage of Pd was measured by ICP-OES.

[0084] (I) Comparison of Sample 1 (Example 1, PdCeMnO prepared by coprecipitation) and Samples 5 and 6 (Comparative Examples 1 and 2, Pd / CeMnO prepared by impregnation) shows that when the transition metal element is Mn, the coprecipitation method (Sample 1) is more likely to obtain higher catalytic activity than the impregnation method (Samples 5 and 6) under the same other conditions. Figure 1 a. Combined with Figure 1 From the X-ray diffraction spectrum given in b, it can be seen that the average particle size of the sample obtained by the co-precipitation method is smaller than that of the sample obtained by the impregnation method, so it has more abundant surface defect sites, namely catalytic active sites.

[0085] (II) Similarly, by comparing Sample 2 (Example 2, PdCeZrO prepared by coprecipitation) and Sample 7 (Comparative Example 3, Pd / CeZrO prepared by impregnation), it can be seen that when the transition metal element is Zr, under the same other conditions, the coprecipitation method (Sample 2) is more likely to obtain higher catalytic activity than the impregnation method (Sample 7). Figure 2 shown.

[0086] (III) Comparison of Sample 3 (Example 3, NaHCO3 as precipitant) and Sample 4 (Example 4, NaOH as precipitant) shows that when other conditions are the same, the effect of using NaOH as precipitant (Sample 4) is better. Figure 3 shown.

[0087] (IV) Comparison of Sample 3 (Example 3, PdCeMnO treated in ethanol) and Sample 8 (Comparative Example 4, PdCeMnO not treated in ethanol) shows that, when other conditions are the same, the reduction treatment of the precipitate in ethanol (Sample 3) is more beneficial to the final catalytic performance than the untreated one (Sample 8). Figure 4 As shown in a. Figure 4 From the X-ray diffraction spectrum given in b, it can be seen that the average grain size of the catalyst treated with reduction in ethanol (sample 3) is lower than that of the catalyst not treated in ethanol (sample 8), so it has more abundant surface defect sites, that is, catalytic active sites.

[0088] Comparison of sample 1 (Example 1, washed with water) and sample 9 (Comparative Example 5, not washed with water) shows that sample 9 has a lower catalytic combustion activity for methane, i.e., the ignition temperature T 10 The ignition temperature of methane on sample 1 is only 380℃. Figure 5 As shown in a. Figure 5 From the X-ray diffraction spectrum shown in Figure b, we can see that the average grain size of sample 9 is 7.2 nm, which is larger than the 5.8 nm of sample 1, and there is obviously a large amount of sodium nitrate residue in sample 9. Therefore, the catalytic performance of sample 9 (unwashed) is much lower than that of sample 1 (washed).

Claims

1. Application of PdCeO-based catalyst prepared by co-precipitation method in methane combustion, characterized by: It is mainly composed of cerium oxide and contains the active component Pd and another or two or more transition metal elements; The transition metal other than Ce and Pd is one or more of Zr, Cu, Mn, Fe, Co, Ni, Ru, Ag, Pt, and Au; In the PdCeO-based catalyst, the mass percentage of Pd is 0.1-5%, and the mass percentage of other transition metals other than Ce is 0.5-50%. 1) Dissolve the precursors of all metal elements including Pd in water simultaneously; 2) adding a precipitant to obtain a precipitate; 3) The precipitate is washed with water and then dispersed into the treatment liquid for further treatment; 4) After drying and calcining, the PdCeO-based composite oxide methane combustion catalyst prepared by the co-precipitation method is obtained; The treatment liquid used is one or both of methanol and ethanol with reducing properties.

2. The use according to claim 1, characterized in that: The transition metal other than Ce and Pd is one or more of Zr, Cu and Mn.

3. The use according to claim 1, characterized in that: The mass percentage of Pd is 0.5 to 2%; the mass percentage of other transition metals except Ce is 5 to 35%.

4. The use according to claim 1, characterized in that: The Ce precursor is at least one or more of cerous nitrate and cerous sulfate, the Pd precursor is at least one or more of palladium nitrate and tetraammine palladium nitrate, and the precursors of other transition metals are at least one or more of nitrates, acetates, and sulfates containing corresponding transition metals.

5. The use according to claim 1, characterized in that: The precipitant is at least one or two or more of sodium hydroxide, sodium bicarbonate, sodium carbonate, ammonium carbonate, ammonium bicarbonate, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide; After adding the precipitant, the overall concentration of the metal precursor reached 0.10 ~ 2.5 mol / L, and the final concentration of the precipitant reached 0.1 ~ 10 mol / L.

6. The use according to claim 1, characterized in that: The stirring time after adding the precipitant is 1 minute to 1 hour; the treatment time of the precipitate in the treatment solution is 1 minute to 1 hour; The mass ratio of sediment to treatment liquid is 1:2 ~ 1:100; The calcination temperature is 350-700°C and the calcination time is 1-5 hours.

7. The use according to any one of claims 1 to 6, wherein the use is use of the PdCeO-based composite oxide prepared by co-precipitation method in the treatment of tail gas containing methane.

8. The use according to claim 7, characterized in that: The PdCeO-based composite oxide methane combustion catalyst prepared by a co-precipitation method is used in the treatment of methane-containing motor vehicle exhaust or thermal power plant exhaust gas, wherein the volume ratio of the reaction gas is: 0.01-2% CH4, 0.05-20% O2; the remainder is N2 or other inert gases.

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